PENTASTOMIDA 523 



p. 407), dog mange may be caught by humans. Whittield and 

 Hobday describe in the Veterinary Journal seventeen cases which 

 have come under their observation. F. V. T.] 



Order. Pentastomida. 

 Family. Linguatulidae. 



Arachtiida greatly altered in consequence of their parasitic manner of life ; 

 for a long time they were regarded as helminthes. The body is elongated, 

 vermiform, flattened or cylindrical, and more or less distinctly annulated. The 

 head, thorax, and abdomen are not defined from each other (fig. 371). The elliptical 

 mouth, surrounded by a chitinous ring, is situated at the anterior end, on the 

 ventral surface, and the intestine leading straight through the body opens at the 

 posterior end. Two retractile hooks are at the sides of the mouth (fig. 372) ; these 

 are usually considered to be the terminal joints of two pairs of legs, but it appears 

 to be more correct to regard them as the remains of the antennae and palpi (Stiles). 

 According to this opinion, the legs in the adult state are completely degenerated. 



The nervous system is reduced to an cesophageal ring. No organs of sense are 

 recognizable except the papillae at the anterior end. There are neither organs of 

 circulation nor of respiration. 1 



The sexes are distinct. In the small male the sexual orifice is situated ventrally 

 in the anterior part of the body ; in the female it is placed near the anus. The 

 Linguatulidcc lay eggs, and from each egg, after being conveyed into an inter- 

 mediate host, a four-legged larva, with rudimentary mouth parts, hatches out. It 

 goes through a series of metamorphoses, and passes through a second larval 

 condition, which, however, possesses the essential characteristics of the fully 

 developed form. Sooner or later it migrates during this stage, and reaches its final 

 host, mammal or reptile, in the nostrils or lungs of which the adult Lingtiatulidcc 

 live. 



[As adults they live as internal blood feeders in various birds, 

 reptiles and mammals, especially in the nasal and respiratory 

 passages. The larval stage occurs in another host in an encysted! 

 condition ; this host is usually an animal preyed upon by the species 

 in which the sexual forms are found. The larvae bore through the 

 walls of the host's stomach and enter liver and spleen or brain, where 

 they encyst ; here they grow until they assume almost the appearance 

 of the adult. These encysted larvae on being eaten later make their 

 way into the nasal passages and lungs, where they mature. Both 

 adults and larvae occur in man, as mentioned later. 



[Three genera are recognized in this family : 



[(i) Linguatula. Body flat, annulated. Adults live in the nasal sinus. 

 [(2) Porocephalns. Body cylindrical, elongate, with often deeply cut rings. Adult 

 in respiratory organs of snakes, larvae in animals and man. 



[(3) Reighardia. Cylindrical, but not ringed. Not found in humans. F. V. T.] 



1 What are designated as stigmata in the Linguatulides are the orifices of sebaceous, 

 glands. 



33 



